1. Field of the Invention
The invention relates to internal combustion engines and, more particularly, to a technique to controlling the intake and exhaust of a combustible fuel-air mixture in a four-stroke internal combustion engine.
2. Description of the Prior Art
In a conventional four-stroke internal combustion engine, a power piston is disposed for reciprocating movement in a cylinder. The upper end of the cylinder is closed by a cylinder head that carries at least one intake valve and at least-one exhaust valve. Upon opening the intake valve and moving the power piston downwardly within the cylinder, a combustible fuel-air mixture will be drawn into the cylinder. After combustion, the exhaust valve can be opened (while maintaining the intake valve closed) and, upon upward movement of the piston, the combusted fuel-air mixture will be discharged from the combustion chamber.
The foregoing construction has been used successfully for years in four-stroke internal combustion engines. Unfortunately, there are serious drawbacks associated with the use of intake and exhaust valves to control the flow of gases into and out of the combustion chamber. As used herein, the word "valves" will mean poppet valves, unless the context indicates otherwise. The drawbacks of intake and exhaust valves are well known and will be described only briefly. A common problem associated with valves, particularly exhaust valves, is their ability to resist the heat of the gases flowing around them. The hot gases can cause the valves to wear rapidly and, in extreme cases, to fail beyond repair. The valves must be made of relatively expensive materials, and they must be made to precise tolerances in order to effect a gas-tight seal at suitable times. Another problem with conventional intake and exhaust valves is that their ability to effect a fluid-tight seal can vary depending upon the temperature of the valves and the surrounding engine components. Yet an additional concern is the noise that the valves can make as they are rapidly opened and closed during operation of the engine. At higher engine speeds, the inertia of the valves may cause them to "float" or fail to close completely, thereby reducing engine performance and possibly leading to catastrophic damage to the engine.
Various techniques are known where intake and exhaust valves are not necessary for use with internal combustion engines, but these arrangements require extreme modification of the engine itself. For example, a two-stroke engine employs a reciprocating power piston without the need for intake or exhaust valves. The intake and exhaust valves are replaced by ports formed in the power cylinder. In such engines, the combustion chamber is closed by a cylinder head that contains only an opening for a spark plug. While two-stroke engines operate successfully, they are noisy, inefficient, and a source of excessive pollution. Thus, they are used only for applications where small, inexpensive engines are required, such as chain saws, leaf blowers, lawn mowers, and the like.
Another valveless internal combustion engine is the Wankel engine. In a Wankel engine, a tri-lobed rotor moves eccentrically within a narrow chamber. The ends of the rotor engage the walls of the chamber so as to create regions of negative pressure and positive pressure, as well as a combustion chamber, during the excursion of the rotor about the chamber. While such a construction has been utilized successfully, Wankel engines are notoriously fuel-inefficient and a source of excessive pollution. Such characteristics are similar to those of two-stroke engines, thereby limiting the usefulness of Wankel engines.
Desirably, a four-stroke internal combustion engine would be available that would have acceptable performance and reliability without the need to use intake and exhaust valves. Such an engine preferably would be quiet in operation, fuel efficient, low in pollution, and powerful.